Fiber optic cables include one or more optical fibers or other optical waveguides that conduct optical signals, for example carrying voice, data, video, or other information. In a typical cable arrangement, optical fibers are placed in a tubular assembly. A tube may be disposed inside an outer jacket or may form the outer jacket. In either case, the tube typically provides some level of protection for the fibers contained therein.
Optical fibers are ordinarily susceptible to damage from water and physical stress. Without an adequate barrier, moisture may migrate into a fiber optic cable and weaken or destroy the cable's optical fibers. Without sufficient protection, stress or shock associated with handling the fiber optic cable may transfer to the optical fibers, causing breakage or stress-induced signal attenuation.
One conventional technique for protecting the optical fibers is to fill the cable with a fluid, a gel, a grease, or a thixotropic material that strives to block moisture incursion and to absorb mechanical shock. Such fluids and gels are typically messy and difficult to process, not only in a manufacturing environment but also during field service operations. Field personnel often perform intricate and expensive procedures to clean such conventional materials from optical fibers in preparation for splicing, termination, or some other procedure. Any residual gel or fluid can render a splice or termination inoperably defective, for example compromising physical or optical performance.
Another conventional technology for protecting optical fibers entails placing a water-absorbent chemical, such as a water-swellable material, within the cable. The chemical absorbs water that may inadvertently migrate into the cable, to help prevent water from interacting with the delicate optical fibers. In one conventional approach, particles of the water absorbent chemical are mixed with the gel discussed above, and the mixture is inserted into the cable. This approach typically suffers from the same handling drawbacks as using a pure form of a gel; the materials are messy and difficult to process.
More and more, users are requesting cable designs that are completely dry and/or are substantially free from greasy gels inside the cable tubes or cable core interstices. Dry cables are much easier to process in the field and are faster to prepare compared to gel filled cables and thus have lower labor costs associated therewith. The all dry cables are typically lower in weight compared to gel filled cables, which adds to ease of installation. One conventional dry cable approach includes applying a water-swellable chemical to the surface of a tape or a yarn that is inserted in the cable lengthwise. If water enters the cable, the water-swellable chemical interacts with the water to attenuate water flow along the cable.
However, many dry cables manufactured with water-swellable tapes and yarns (e.g., Super Absorbent Polymers, or SAP), are limited in that they can not withstand water with high concentrations of ions (e.g., saltwater or seawater) and may not perform adequately against other types of soiled water (e.g., water containing oil, detergents, sewage, etc.). Furthermore, water-swellable tapes and yarns become too costly as the physical size of the cable and the free area inside the tubes increases. Moreover, the SAP's utilized by water-swellable tapes, yarns, and foams are expensive and known to degrade in the presence of ionic solutions. Especially for larger cable designs (for tube sizes over about 10 mm in diameter), the cost of water-swellable tapes, yarns, and foams is high and the water blocking performance is low.
Accordingly, to address these representative deficiencies in the art, an improved capability is needed for protecting optical fibers from water damage. A capability addressing one or more of the aforementioned needs, or some related need in the art, would provide robust fiber optic installments and would promote optical fibers for communications and other applications.
Many aspects of the invention can be better understood with reference to the above drawings. The elements and features shown in the drawings are not to scale, emphasis instead being placed upon clearly illustrating the principles of exemplary embodiments of the present invention. Moreover, certain dimensions may be exaggerated to help visually convey such principles. In the drawings, reference numerals designate like or corresponding, but not necessarily identical, elements throughout the several views.